


INSANE (one shot)

by Nightingale_girl



Category: Undertale
Genre: Backstory, Bad Jokes, Bad Puns, Dark, Entry seventeen, Family, I'm Bad At Tagging, Laboratories, Mistakes, My First AO3 Post, One Shot, Other, Pre-Undertale, Responsibility, What Have I Done
Language: English
Status: Completed
Published: 2018-11-29
Updated: 2018-11-29
Packaged: 2019-09-02 07:03:16
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,764
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16782013
Author URL: https://archiveofourown.org/users/Nightingale_girl/pseuds/Nightingale_girl
Summary: "Don't forget."You tell yourself that every day, but even then sometimes you find it slipping away, fading from your memory. Another empty echo."Don't forget!"It's in the photo; the only physical reminder you had that kept you a believer. That stopped you from forgetting."Don't forget..."His name. It's W. D GasterA one-shot book, as in only one chapter. I'll continue it if many people request for it to be continued (highly unlikely) or if I suddenly get a stroke of inspiration (also unlikely).I got inspired from a story to write this, so I hope this chapter inspires you, whoever you are, as well! Yeah, that sounds cool, a chain of inspiration... And this is my first work on ao3. How do I tag?!Anyways, 'You' are Sans. Hope you enjoy it :)





	INSANE (one shot)

**Author's Note:**

> One shot, as in one chapter. I'll continue if many people request for it or if I suddenly get inspiration to.

**Heads up!  
'You' are Sans.**

***

Gaster had never been a good father, you'd think.

It was common that he'd leave you and Papyrus with no warning whatsoever, only to return weeks later, claiming that it had been an emergency, that it had been important.

Important? So Papyrus and you weren't important?

With the way Gaster spoke and acted, you honestly wouldn't have been surprised if he actually thought that. Gaster always spent a significantly larger number of days more working than he ever did with the two of your. He would hole himself up in his sacred lab, scribbling notes and mumbling gibberish about his precious experiments, conveniently forgetting about his two sons at home alone.

Gaster was a bad father, and you hated it.

You hated it, not him. You couldn't bring yourself to hate Gaster whenever he actually came home. He would sweep through the doors, apologetic and occasionally sheepish smile already on his face. You would always feel the same cold bitterness in your soul. If Papyrus ever felt the same, he never expressed it, or even showed any hints of hurt in his happy smile.

Papyrus would always drop whatever he had been doing (literally. Once he dropped a brick onto your foot-You were still salty about that) and bolt to the door, joyfully leaping into his father's open arms. Gaster would then apologise for leaving for that period of time, usually giving a flimsy excuse. (flimsy to you, sincere to Gaster, acceptable to Papyrus.) Papyrus would then wave away all his apologies, instead focusing on the oh so important fact that Gaster was back. During these periods of time, you would often lurk in the background, sending death glares towards your 'father'.

He wasn't a good father, you would repeat firmly to yourself, forcing yourself to recall how you and your baby brother has struggled while he had been away. You would replay every bad memory as some sort of masochistic reminder whenever Gaster tried talking to you, whenever he gave you a sad but patient smile.

And yet, after a day or two, three being the record, you would find yourself giving in. You would unknowingly smile and chuckle at Gaster's jokes and puns, (yes, Gaster loved jokes, puns especially. Papyrus supplied plenty of groans while you would try to hold back your laughter.) You would return his hugs, you would listen with wide sockets at Gaster's bedtime stories of the interesting experiments he conducted in his lab, you would... You would love Gaster back.

You would love your father back.

And your house would be full of merry laughter. Delicious smells would wander out of the kitchen, tempting you out of your bed only to see Gaster cooking a storm, more often than not with Papyrus hovering at the side observing intently. (Once he tried to teach Papyrus how to make spaghetti, since the little skeleton had seemed so enraptured with the pasta after he cooked it. Papyrus had... Burnt down the kitchen, but Gaster had just waved it off, assuring the small skeleton that his skills would improve with time and practice.)

All in all, everything would be good. Everyone would be happy. Gaster would be there to provide a responsible father figure for Papyrus.

This time Gaster seemed to be staying particularly long. He usually stayed for around two weeks, three if you were lucky, before disappearing as abruptly as he had came. You would then spiral down the usual cycle: You would be shocked, hurt, disappointed. You would lock yourself in your room, wondering why he left. Were you not good enough? Did you behave poorly? What did you do that caused your own father to leave yet again?

That was always the most painful part. You would tilt your skull towards the ceiling, comparing the sound and atmosphere again and again, how it had been noisy and cheerful not too long ago, how dark it suddenly seemed; how deafening the silence was. You would wallow, silently begging for your Dad to come back, to say it was just another one of his pranks, that he only needed to check on something.

After what felt like an hour or two, (In reality was actually at least half a day) you would feel anger. You would be bitter, even disgusted with Gaster. Father? HAH! You would mumble curse words (you picked them up from the time Gaster had dropped a whole pan of fried rice onto the floor. He had grumbled a few words of choice while you blinked at him from behind. He had warned you to not use them, after realising you had witnessed everything. You listened. Sorta. You just got a sick sense of satisfaction from disobeying his wishes whenever he abandoned you and Papyrus) under your breath, punching your pillow in a rage.

Then would come the grudging acceptance. Gaster needed to work. He would be back soon. You would sulk at the wall, suddenly feeling drained from all the emotions and thoughts from earlier. Usually at this point, Papyrus would knock softly (soft knocking to him. Loud frantic bashes to you) on your door. He would ask you if you knew when Dad would be back, sadness evident on his skull. You would hug your baby brother, suddenly shameful of your behavior from earlier, but you would never respond. 

(When did it happen? When did Papyrus stop asking? When did he... Give up?)

And your would slip back to your usual habits, as your patiently waited for Gaster to come back. It would become an unspoken agreement, the thing your both silently looked forward to, for Gaster to come home. And just when your would begin to slip back to being used to forced independence, Gaster would suddenly return. Like the rainbow with the sunshine after the storm.

And the cycle would repeat.

This time, Gaster was staying for a shockingly long time. It was over a month, and yet your Dad showed no signs of departure. You had avoided confronting him in fear of disappointment, in fear of acknowledging the inevitable.

But now...

"WOWIE, DAD!! THESE PANCAKES ARE INCREDIBLE!!" Papyrus exclaims, happily tucking into the large stack of pancakes liked before him. Gaster chuckles, adding a healthy dose of honey to his stack. "Why thank you, Paps. I'm glad that my cooking satisfies you."

You don't comment. Instead, you hum in agreement. You smile at the fluffy pancakes, realising what they were missing. "hey paps," you grin.

"YES BROTHER?"

"can you pass me the ketchup?"

"...!" Papyrus makes his classic annoyed face, heh. "BROTHER, NO! HOW- WHY! KETCHUP IS NOT FOR PANCAKES!!" He whines passionately, stubbornly refusing to pass the bottle. Papyrus disapproves of your love for ketchup, which you understand. It just happened that each meal seemed incomplete without the condiment.

Gaster chuckles, shaking his head. "Sans, don't annoy your brother," he scolds half heartedly. He reaches over and hands you the red bottle, much to Papyrus's displeasure. Gaster watches as you squirt on a generous amount of ketchup on your pancakes. His sockets suddenly light up, and you grin, recognising the tell tale sign of his next words.

"Really, sans. Can't you see your ketchup obsession is _eating_ at Papyrus?" Gaster grins.

"YES! NOT ONLY IS IT BAD TABLE MANNERS BUT... WAIT..." Realisation dawns in Papyrus's eyelights and he looks at Gaster with utmost betrayal. "DAD!!! HOW COULD YOU?!" Papyrus groans.

You laugh, finishing your last bite of ketchup and pancakes. "geeze, dad, how am i supposed to ketchup?..." You trail off, realising what you just said.

Gaster doubles over in laughter, wiping imaginary tears from his sockets. Papyrus looks at you in horror. "NOT YOU TOO!!" He gasps.

"Sans! I'm so proud of you!" Gaster chokes out. You feel like your face is splitting apart from the wide smile. It still made you unbearably proud whenever Gaster complimented you.

"But seriously- we should lay off on the puns. We're being a bit too _pun_ ishing on your brother," Gaster winks, shooting your finger guns. "NYEH!!!!" Papyrus stands up from his chair. "TELL ME WHEN THE AIR STOPS BEING TAINTED WITH HORRIBLE HUMOR!!" 

"but'cha smiling," Sans points out cheekily. Papyrus sweeps off, grumbling loudly. "I KNOW... AND I HATE IT!! The seven year old skeleton grunts over his shoulder as he leaves the kitchen.

Gaster chuckles, standing up and collecting the plates. You let him take your plate, glancing at him in appreciation. Whenever your were alone, you were the one with the responsibility of washing the dishes, and it was no fun task. Talking about when your were alone...

"dad?" You say, standing up from your chair and following him to the sink, all traces of humor on your skull gone. Gaster pauses at your serious tone. "Yes?" He prompts, already knowing what you were going to say. It was the elephant in the room you had been avoiding on addressing.

"it's paps' birthday tomorrow... and i know you've already stayed longer than usual, and i appreciate that. but... can you stay for just one more day? i know you have work and all, but Paps will be so happy if you're there for his big day..." You mumble, avoiding Gaster's eyelights. There was a loud silence in the kitchen, save for the sound of the occasional plate being placed back on the rack. Finally, after what seems like an eternity, Gaster turns to you, sighing.

"Sans... I'm sorry."

Your non-existent blood runs cold and you lower your gaze to the floor. Maybe that had been a cowardly excuse, saying that it was for your brother's sake. You didn't want him to go, Papyrus's birthday had just been an add on-

"... Do you remember entry Seventeen?"

You look up from the floor, caution creeping into your soul. "yeah..." You couldn't forget even if you tried...

_You look at the board where Gaster was scribbling on. It had been a rare chance today, that Gaster allowed you to watch him take notes. You were often amazed at your father's intelligence, as he scribbled down various formulas effortlessly. Your soul would swell with pride... This was your Dad._

_Today, however, he seemed to be stuck. Gaster was mumbling incoherently to himself as he looked over his workings with tired eyelights. "I don't get it... Where did it go wrong? It should be running smoothly!"_

_You stare at the board overflowing with numbers arranged in elaborate formulas. Your eyelights scan the workings before flitting back to your father. "i don't understand," you say slowly._

_Gaster looks back at you, a tired smile crossing his features. "It's okay, Sans. It's hard to get it. I'm already impressed you show interest in these type of things..."_

_You shake your skull adamantly. "no... not that. i don't understand why you subtracted the negative number over the fraction when it should've been the positive square..."_

_Gaster stared at the board, then stares at you. He starts chuckling lowly, burying his skull in his hands. You blink at your father, wondering if you had broke him. "what's so funny?" You ask defensively. You had honestly thought your calculation was correct. Gaster shakes his skull in... Disbelief?_

_"Sans! This... How did you? I can't believe I missed that! And I don't remember teaching you that formula! How...? Sans, you're a genius!" Gaster exclaims, looking at you proudly. You feel yourself perk up at his praise._

_Gaster looks back at the board, seemingly considering something. After a few moments, he turns to you. "Sans... How would you like to see my latest experiment?"_

_You freeze. His latest experiment...? "really?!" You ask in shock. Gaster never allowed you to even peek at his projects, saying that it was far too dangerous and that you wouldn't understand them anyways. "Yes," he replies, smiling. "I trust that you are mature enough to not mess with dangerous stuff, and I think you have a lot of potential to become a scientist as well!"_

_You grin, sockets lighting up. "okay!"_

***

_"Sans, this is Alphys. Alphys- Sans, my son."_

_You stare at the small lizard sweating bullets before you, clutching her clipboard as if her life depended on it, nervously avoiding eye contact. "hello," you say._

_"H-Hi," Alphys squeaks, hiding her face behind her clipboard. You tilt your skull at her.... What a strange monster._

_"Sans, today I'm bringing Alphys along to see my latest experiment as well. She's very smart as well, and has a very promising future!" Gaster gushes. Alphys seems to shrink further at his words, practically quivering under your look. "right..." You say, wondering if Alphys was actually as smart as Gaster claimed._

_"Anyways, follow me you two!!" Gaster spins on his heels abruptly. You and Alphys scramble to catch up with the scientist, attempting and failing to match his long strides. Your pass by many rooms, with all the doors having signs such as 'employee only' and 'scientist only' and sometimes 'don't even think about going in unless you're gaster'. Your finally stop in front of an unmarked door. Gaster opens the door after tapping in a elaborately password. You and Alphys hesitantly follow him inside..._

...

_There... Were no walls?_

_You blink in surprise. The three of your were walking on a built platform, with unfinished railings. Gaster stops at the end of the platform, turning to face your. "Careful- there isn't railing over here," he quickly reminds. "Now... Do you see the infinite darkness before you?"_

_Surprisingly, Alphys answers before you can. "Yeah... How is this possible?" She wonders, eyes wide. You glance at her, noticing the lack of stutter. You look back at your Dad, only to freeze at the look on his face. There was... A look of intense hunger and curiosity on his face. Gaster seemed to not hear Alphys's question. Instead, he was staring ahead at the darkness that stretched forever..._

_"Dark. Darker, yet darker."_

_"The darkness keeps growing, the shadows cutting deeper."_

_"Photon readings are negative."_

_This next experiment seems"_

_"Very"_

_"Very"_

_"Interesting."_

_"..."_

_Gaster turns around, face unreadable._

_"What do you two think?"_

***

_"i... i don't want to go back."_

_You look down at the floor, frowning. It had been.... Interesting. But... The cold feeling you got when you heard Gaster..._

_It made your soul quiver._

_Gaster was quiet for a few seconds. "Ah..." he finally says. "I suppose you may have been a bit intimidated by the void. Its alright, I understand. Maybe next time."_

_You nod, staring at the script before you. Gaster had been working on these strange symbols. Among the many shapes, you could make out little faces, arrows and so on. It was your dad's secret code._

_Wing dings is what he called it._

"You remember the void, then? Well, no matter what I do, I haven't been able to make much of a breakthrough... Hence, I can safely promise you that I will be staying for at least one more week-" you cut Gaster off by suddenly hugging him. Gaster chuckles, petting your skull. You press harder into him, listening to the way his ribcage vibrates when he laughed...

"thanks..." You whisper, burying your skull into his shirt.

"No problem, Sans."

***

You smile, standing up from your chair.

It was unusually late for you to be up, but you had stayed up working on your brother's present: a bright red scarf that seemed to describe your brother's personality.

You glance at your bare wrist, wondering if Gaster was still awake. Maybe you could show him the scarf? You go out of your room, clutching the scarf. You hum as you make your way over to Gaster's room, opening the door...-

Empty. The room was empty, the messy papers strewn across the desk gone. As if he had never been there...

The scarf drops to the ground, your fingers taut from shock and... Betrayal.

He promised.

The sound of a door slamming interrupts your thoughts. Your skull snaps up and you let out a growl.

Gaster.

Dashing to your room, you stuff on the first shoe wear you spot- fluffy pink bedroom slippers. Throwing on the faded blue jacket Gaster has given you last Giftmas, you throw open the door and chase after your Dad, determination thumping in your soul.

***

Gaster strode down the halls, clenching his teeth.

The experiment... Was falling apart. The constructed platform was breaking apart, and one of the scientists had just called him to inform him that within an hour, Asgore would be coming over to officially declare the project unsafe. That wouldn't do... He had important notes he had left there. Gaster just needed to retrieve those notes so all that time wouldn't be a waste...

He quickly typed in the passwords and entered, leaving the door open. (He would be in and out in a second, he didn't need to close the door. Later, Gaster would regret that small hasty decision. If only he had shot the door...)

He failed to notice the figure running after him.

Gaster looked sadly at his first ever failed experiment as he collected the papers. The paper rustle as Gaster gazed around. Even now he could see the platform was practically crumbling. It wouldn't be safe to hold more than two people-

"DAD!!"

Gaster froze. No way... He looked behind him slowly, sockets wide. He... Had never heard you raise his voice before...

But what was more important was that you were here. With him. On the platform. That was breaking apart...

Crap. 

"Sans, it's not saf-"

"gaster, you promised! don't you care about papyrus at all? don't you care about me?!" You scream, tears running down your face. "you promised!!" You jab a phalange, glaring at Gaster, chest rising and falling heavily; you were still panting from running here.

Gaster stared at you. So that's why you were here... And why you were so angry.

"Sans, you need to get out, it's not-" a loud groan from the platform interrupts Gaster. Suddenly-

SNAP!!

You look up to see a chunk of metal falling towards you. Dust was already caking the air as the ground collapsed around-

Something slams into you and you stumble back, out of the room where the door hadn't closed. Time seemed to slow down as you look up to see...

Gaster staring at you, hands outstretched as he...

Fell into the Infinite darkness with the debris and metal, Into the void.

What...?

Your skull was throbbing from when it had hit the wall... Your vision was blurring.... You sink to your knees... 

***

The first thing you see is white. For a moment you panic, wondering if the void has changed colours. Then you pause, trying to recall why the void had been the first thing you considered...

Than you remember.

You, stubbornly screaming at your Dad in a blind rage as tears clouded your vision. Your Dad (Gaster... Why was it suddenly difficult to think his name?) trying to warn you that it's wasn't safe. You, interrupting him. You, about to get crushed by a metal structure...

Gaster, sacrificing himself to save you.

Your Dad, disappearing into the void.

You sit up frantically, chest heaving and your magic crackling wildly-

"SANS!"

"S-Sans? Y-You're awake!"

You freeze, turning your skull as you recognise the voices. "papyrus! alphys, you need to go to the void! dad fell in there and we need to save him..." You clutch your skull as sudden ringing pain attacks it. You grimace, glaring up. "we need to..."

"S-Sans, calm d-down! Your skull i-is still hurt," Alphys rather forcefully pushed you back into a lying position on the... Hospital bed? "YES, SANS! YOU ARE VERY LUCKY TO REGAIN CONSCIOUSNESS WITHIN SUCH A SHORT PERIOD OF TIME!"

You struggle feebly against Alphys's hold. They didn't understand!! Gaster... He needed to be reached! If your moved fast enough, maybe...

"SANS, STOP MOVING!!" Papyrus cries. "AND WHO IS THIS 'DAD' YOU SPEAK OF?"

You freeze at that. Did Papyrus... Wha...?

"T-The two of y-your have a d-dad? But... I th-thought your had no l-legal guardian!"

"NO, WE DO NOT HAVE ANY FATHER, SANS MUST BE DREAMING!"

You shake your skull adamantly, your struggling faltering as you suddenly feel the first strokes of lethargy. "remember dad? gaster, the royal scientist!"

You can already feel your vision blurring as Alphys looks at you in worry, fidgeting nervously with some paperwork. "B-But... There is no Royal scientist..."

***

No one knew what you were talking about.

Gaster? Who's that?

After they finally discharged you from the hospital, you had been frantic, stopping every monster in sight, demanding that they tell you where Gaster is, pleading them to remember your father.

You realised after a while that falling into the void caused the monsters around Gaster to forget his very existence. You, for an unknown reason, were able to retain your memory of him. Maybe it had been because you were the closest to him and the void when he fell inside. Maybe it was because you had witnessed him dying. (Dying? Could you even call it that?)

Even Papyrus insisted that Gaster was just a figment of your imagination. All those months of doubting your father's existence... You would probably have accepted that you had just dreamed it all up if it weren't for it. 

It had been Papyrus's first Giftmas that day. The small babybones had been bundled up in his blanket when your Dad had suggested taking a photo. You had been reluctant to agree at that time. (You hadn't liked being in photos. You still don't) Now, you were infinitely grateful for it.

Your father... Hadn't been the best father. Some, like you had, may even consider him a bad father. But he was your father.

And he had sacrificed himself for you.

If only you had stopped to listen to his iinstructions that day... If only... 

No matter what, he was gone now, and you could barely remember his face without reference to the photo. 

C'mon, think! Remember! Gaster was the Royal Scientist... He liked puns and jokes... He loved you and Papyrus...

"Don't forget."

You tell yourself that every day, but even then sometimes you find it slipping away, fading from your memory. Another faded echo.

"Don't forget!"

It's in the photo; the only physical reminder you had that kept you a believer. That stopped you from forgetting.

"Don't forget..."

His name. It's W. D Gaster

W. D. Gaster? Who's that? They laugh, they joke, they whisper, pity and confusion in their voice.

His name! Its W. D. Gaster!

No one remembers, and you feel yourself slowly going Insane.

**Author's Note:**

> I know with the release of Deltarunes, there is a high chance this story is all wrong, but I wrote this anyways. I just wanted to write about how Sans became the skeleton we all know, and how Gaster 'disappeared'. 
> 
> Anyways, (shameless self promo) I'm on Wattpad and Quotev under the same name! I have a skeleton harem (yes, I'm crazy for these stories) written on Wattpad, while my Quotev account is basically as bare as this. 
> 
> How do I tag-
> 
> Basically, hope you enjoyed this! Don't forget to comment/kudos!


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